Siemens SIMATIC S7 F Manual page 85

Programming
In addition, fail-safe blocks are also available for standard functions such as
arithmetic, logic, multiplexing, etc. You can find a complete list of the fail-safe
blocks in Appendix.
•
F Control blocks are automatically inserted during compilation and are never
to be inserted by user.
F Control Blocks
F_CYC_CO
F_M_DI4
F_M_DI8
F_M_AI6
F_M_DO10
F_M_DO8
F_PLK
F_PLK_O
F_TESTC
F_TEST
F_TESTM
F_SHUTDN, DB_INIT,
RTG_LOGIC,
FAIL_MSG
•
Simulation blocks (F-simulation blocks) that are used in the offline simulation
of the Safety Program with PLCSim 5.0. PLCSim 5.1 does not use the
simulation blocks.
Libraries with Different Versions
Several versions of the "Failsafe Blocks" library can exist on a programming
device/engineering system at the same time. However, a Safety Program can only
contain blocks of the same version. Programs that contain blocks from libraries
with different versions cannot be compiled.
Fail-Safe Systems
A5E00085588-03
Function
F cycle time monitoring
Fmodule driver for PROFIsafe communication with F-I/Os
Logical program execution monitoring and data flow monitoring
Monitoring of the self-tests of the operating system
Self-tests executed in each cyclic interrupt cycle
Switching of safety mode on and off
Safety Program shutdown and restart logic blocks
5-3